65 to 67 maybe, but there was major changes in 68-69

Dont know about 66 as well, but I had a 64 Catalina as a kid, wiped out both fenders and was told by a local service station owner who sold me a 64 Bonneville for the front clip that they were the same .it went on,.... But it wasnt quite right.

according to an article in the above magazine, the 65 and 66s are interchangable. 67 had a new body design. also the 66 star chief executive is on a 124 inch wheelbase, same as the bonneville. the catalina and grand prix however are on a 121 inch w/b. whether that makes a difference in body panels i don't know.

it also only lists variations of the 389 and 421 v-8'* as options. i'm guessing if it has a 400 cube the motor has been switched with one from a later date.

also lists 45,212 executives as built in 66.

hope that helps
bil